Abstract

The latest scanning transmission electronmicroscopes (STEMs) are able to resolve and analyze individual atoms, matter’s basic constituents. Unlike scanning tunneling microscopes, they are able to look inside materials. They can alsodetermine the atomic composition and other properties by spectroscopic means. The last two decades brought two developments that made electron microscopesespecially powerful: working aberration correctors allowed the spatial resolution to be improved by about 3x, and newly developed monochromators and spectrometers allowed the resolution of electron energy loss spectroscopy (EELS) carried out in an EM to improve to around 3 meV. The developments have made it possible to image individual atoms in a wide variety of inorganic materials with ease, and their chemical and vibrational properties to be determined. Examples include monolayer materials such as graphene and BN, in which every atom can be resolved and single atom impurities identified, and determining the vibrational properties of a single impurity atom.Related developments have allowed biological materials to be analyzed in a damage-free way by aloof spectroscopy, phonons arising at defects to be detected, and phonon dispersions to be mapped in nm-sized volumes. Nion has played a pivotal role in all these advances. My talk will review how they came about, and illustrate them with practical examples. It will also pay tribute to EM research carried out in Cambridge in the 1960s to 1990s, which foresaw several of the key developments.